Methods of producing oriented high density polyethylene

Abstract

In a method of producing uniaxially oriented polymer material, particularly a uniaxially oriented film, from a high density polyethylene, in which the material is put under tension and is drawn from a transverse heated portion with a draw ratio of 5:1 or higher (preferably 7:1 to 20:1), the drawing temperature is selected to be between 80° C. and 110° C., and preferably below 105° C., whereby excellent gas barrier characteristics are obtained in the drawn material.

We claim: 
     
       1. A method of producing a uniaxially oriented polymer film, in which a high density polyethylene sheet material having a density of 0.94 gm/cm 3  or higher is transported continuously between respective sets of tensioning rollers and drawing rollers and is heated by passing it around a part of the circumference of a tubular metal heating member which is heated internally and is disposed in the atmosphere transversely to the drawing direction between the respective sets of rollers, whereby to heat a portion of the sheet material extending transversely across the full width of the sheet material and to induce drawing of the polyethylene sheet material to take place preferentially in or adjacent to the heated transverse portion, the drawing tension being controlled to draw out the polyethylene sheet material with a draw ratio of 5:1 or higher, and the temperature of the heated portion being selected to be in the range of 80° C. to 110° C. 
     
     
       2. A method according to claim 1, wherein the heating is controlled to maintain the temperature of the heated transverse portion in the range from 80° C. to 105° C. 
     
     
       3. A method according to claim 1, wherein the draw ratio is between 7:1 and 20:1. 
     
     
       4. A method according to claim 1, wherein the tubular metal heating member is heated by passing a heated liquid through it. 
     
     
       5. A method according to claim 1, wherein a fixed metal tube or drum is used as the tubular metal heating member. 
     
     
       6. A method according to claim 1, wherein a hollow metal roller is used as the tubular metal heating member. 
     
     
       7. In a method for producing a uniaxially oriented high density polyethylene film wherein the film is continuously transported in a longitudinal direction through a drawing zone between respective sets of tensioning rollers and drawing rollers and drawing is induced in the longitudinal direction in the zone at elevated temperatures, the improvement comprising passing a high density polyethylene sheet material extending in the longitudinal direction and transverse thereto and having a density of 0.94 gm/cm 3  or higher through a drawing zone consisting of at least one tubular heating member heated internally and disposed transversely to the drawing direction between the respective sets of rollers, the material continuously passing into contact with the tubular heating member and being heated, the sheet material in contact with the tubular heating member being heated transversely across from edge to edge to a temperature of from 80° C. to 110° C. to induce longitudinal drawing preferentially in and adjacent to the transversely heated material in contact with the tubular heating member, the drawing being controlled to give a draw ratio of 5:1 or higher and to impart improved gas barrier and weathering resistance characteristics to the high density polyethylene material.